1. Field of the Invention
The invention relates to a driving device, more particularly to an ultrasonic driving device with current limiting protection.
2. Description of the Related Art
Ultrasonic cleaners are cleaning devices that use ultrasounds (above 20 kHz) to excite a cleaning liquid in which articles to be cleaned are immersed.
FIG. 1 illustrates an ultrasonic driving device 3 employed in a conventional ultrasonic cleaner. The ultrasonic driving device 3 includes a signal generating module 31, an output module 32, an ultrasonic transducer 33, and a high voltage source module 34. The signal generating module 31 provides an alternating current first drive signal (Vd1).
The high voltage source module 34 receives a first alternating current power signal (Vac1) from a commercial power source, and adjusts the voltage of the first alternating current power signal (Vac1) to result in a second alternating current power signal (Vac2).
The output module 32 receives the first drive signal (Vd1) and the second alternating current power signal (Vac2), and adjusts the amplitude of the first drive signal (Vd1) to result in a second drive signal (Vd2) that is provided to the ultrasonic transducer 33.
The ultrasonic transducer 33 is immersed in a cleaning liquid and is responsive to the second drive signal (Vd2) to produce ultrasounds, the frequency of which corresponds to that of the second drive signal (Vd2). The amplitude of the second drive signal (Vd2) is normally within the range of 200-500 volts so as to be able to drive the ultrasonic transducer 33 to produce the ultrasounds.
The ultrasounds produced by the ultrasonic transducer 33 in the cleaning liquid result in ultrasonic vibrations that correspond in frequency to the ultrasounds. Due to the viscosity of the cleaning liquid, the ultrasonic vibrations generate microscopic cavitation bubbles in the cleaning liquid. When the microscopic cavitation bubbles break upon contact with surfaces of an article immersed in the cleaning liquid, the energy released thereby can clean debris from the surfaces of the immersed article.
However, since the ultrasonic transducer 33 is disposed in the cleaning liquid, if an electric leak is present in the ultrasonic transducer 33 due to degradation of or damage to the ultrasonic transducer 33, the user is exposed to the risk of being electrocuted when removing the cleaned article from the cleaning liquid. Moreover, when the ultrasonic transducer 33 is damaged, a large electric current can flow therethrough and can damage the output module 32. The prior art is devoid of any mechanism that can prevent the output module 32 from providing the second drive signal (Vd2) to the ultrasonic transducer 33 when an excessively large current flows through the ultrasonic transducer 33.
In addition, since the amplitude of the second drive signal (Vd2) should be within the range of 200-500 volts so as to be able to drive the ultrasonic transducer 33 to produce the ultrasounds, the output module 32 includes numerous power components to achieve the desired voltage range for the second drive signal (Vd2). Since the power components are likely to break down during use, there is also a need in the art to limit electric current supplied by the high voltage source module 34 to the output module 32 in the case of abnormal operating conditions.